This invention is related to a system which controls the amount of an additive being injected into a main stream of fluid and more particularly to a system which regulates the additive injection by timing circuits.
The preparation of fluid chemical products often requires that a fluid additive necessary to the final product be injected into a main stream of another fluid. In the petroleum fuel industry, fluid injection is required in a number of areas. One example is the addition of odorants, such as mercaptans, to odorless gases, such as liquid propane, to warn users of dangerous gas leaks. Another is the addition of anti-oxidants and dyes to gasoline.
In most cases, it is necessary to precisely control the proportion of additive volume to main stream volume for two reasons. First, the additive fluids are usually expensive and must be carefully conserved. Second, a specified minimum amount of an additive must be added to perform the desired function. In the case of liquid propane, for example, Federal safety regulations presently require a minimum of 217 cc. of mercaptans per 100 barrels of propane.
One method of measurement is the loss-in-weight principle exemplified by U.S. Pat. No. 3,452,774 by Stanton. Stanton discloses a flow control system that uses a conventional process controller having normal proportional and integral functions to compare the loss in weight of a tank holding the fluid being injected. The loss-in-weight method is particularly useful where highly viscous fluids are being measured.
A second method of metering an additive fluid is the quantum-volume principle which uses a freely movable piston that is driven back and forth within a liquid-filled cylinder by hydraulic pressure provided by the metered liquid itself. Each piston stroke provides an amount of liquid equal to the volume of the piston stroke.
Many fluids must be carefully confined within the handling and injection systems due to their polluting effects. Low viscosity liquids, such as the anti-oxidants and dyes, that are used in the preparation of gasoline and the odorant liquids, such as mercaptans, that are used to odorize fuel gases that are difficult to confine. The systems that use reciprocating pumps as in Stanton and those that use free-piston metering devices contain rotary and reciprocating shafts that require seals to insulate the liquid chamber from the atmosphere. Although leakage is usually not large, even a small leakage of odorants or dyes is objectionable. In addition, the seals are subject to wear, which causes further leakage, and must be frequently replaced.